Background crystal oscillator calibration

ABSTRACT

System and method for temperature-calibration of a crystal oscillator (XO) in a mobile device. A temperature-calibration status of the XO is determined and a trigger condition related to temperature-calibration of the XO is detected. If the temperature-calibration status of the XO is not fully temperature-calibrated or if the XO has not been previously temperature-calibrated, a temperature-calibration session is initiated by an XO manager based on the condition, wherein a receiver is configured to receive signals and temperature-calibration of the XO is performed in a background mode based on the received signals. The condition based triggering ensures that the XO is temperature-calibrated prior to launch of any position based or global navigation satellite systems (GNSS) based applications on the mobile device. The trigger condition can include first use or power-on, charging, presence in an outdoor environment, variation in operating temperature, pre-specified time, and/or user input pertaining to the mobile device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application for patent is a Continuation of U.S. patentapplication Ser. No. 15/881,685 entitled “BACKGROUND CRYSTAL OSCILLATORCALIBRATION” filed Jan. 26, 2018, which is a Continuation of U.S. patentapplication Ser. No. 13/784,046 entitled “BACKGROUND CRYSTAL OSCILLATORCALIBRATION” filed Mar. 4, 2013, now U.S. Pat. No. 9,907,035 issued Feb.27, 2018, which claims the benefit of U.S. Provisional Application No.61/666,307, entitled “GNSS BASED CRYSTAL OSCILLATOR CALIBRATION” filedJun. 29, 2012, each of which are assigned to the assignee hereof, andexpressly incorporated herein by reference in their entirety.

FIELD OF DISCLOSURE

Disclosed embodiments are directed to field calibration of a crystaloscillator (XO).

More particularly, exemplary embodiments are directed totemperature-calibration of an XO performed in a background mode usingassistance from one or more wireless signals of known or determinablefrequency, wherein the temperature-calibration is triggered by one ormore exemplary conditions, events, or mechanisms.

BACKGROUND

Global navigation satellite systems (GNSS) are well known inapplications related to tracking and positioning. GNSS systems such asglobal positioning systems (GPS) are satellite-based systems used forpinpointing a precise location of a GNSS receiver or object capable oftracking satellite signals. With advances in GNSS technology, it ispossible to locate and track movements of an object on the globe.

GNSS systems operate by configuring a GNSS satellite to transmit certainsignals which may include pre-established codes. These signals are basedon a GNSS time or satellite time derived from an atomic clock orsatellite clock present in the satellite. The transmitted signals mayinclude a time stamp indicating the time at which they were transmitted.A GNSS receiver, which may be integrated in a handheld device, is timedby a local clock located at the receiver end. Ideally, this local clockis synchronized to the satellite clock (also known as the GNSS time).The device comprising the GNSS receiver is configured to estimate theGNSS time based on the satellite signals in order to synchronize theirlocal clocks to the GNSS time. Once the local clocks are accuratelysynchronized, the device is configured to calculate the propagation timefor the satellite signals to reach the receiver, based on a differencebetween the time at which the signals were received, and the time atwhich they were transmitted. This propagation time is an indication ofthe distance between the satellite and the device, keeping in mind thatfactors such as atmospheric conditions may affect the propagation time.

In order to pinpoint the location of the device, the device performs theabove process to calculate the distance to two or more other satellites(if altitude and/or local time of the device is known, the location canbe determined with a total of three satellites, otherwise, a total offour satellites may be needed). Using the distances to the satellites,it is theoretically possible to “trilaterate” the position of thedevice. However, practical applications diverge from theoreticalexpectations due to several sources of inaccuracies inherent in GNSSbased positioning.

One source of inaccuracy relates to synchronization of the local clock.In modern devices comprising GNSS receivers, time is typicallymaintained via a temperature-compensated crystal oscillator (TCXO), tomaintain the frequency stability required for GNSS operation acrossvarying device temperatures. Even small errors in frequency may resultin large positional errors in position estimation. Thus, the TCXO and/ora voltage controlled temperature compensated crystal oscillator (VCTCXO)have been used in the art to maintain nearly constant frequency acrossfluctuating temperature and voltage. While the TCXO and VCTCXO may alsoexperience some fluctuation in frequency with fluctuations intemperature and voltage, the frequency variations in an XO, i.e., acrystal oscillator without such temperature or voltage compensation, ismuch larger. Accordingly, the XO has historically not been used becauseof the large frequency variations across temperature and voltage thatmay prolong GNSS searches or cause them to fail.

SUMMARY

Exemplary embodiments of the invention are directed to systems andmethods for calibration of crystal oscillators (XO) in a backgroundmode.

For example, an exemplary embodiment is directed to a method oftemperature-calibrating a crystal oscillator (XO) in a mobile device,the method comprising: determining a temperature-calibration status ofthe XO, detecting a trigger condition related to temperature-calibrationof the XO and if the temperature-calibration status of the XO is notfully temperature-calibrated, initiating a temperature-calibrationsession, wherein the temperature-calibration session comprises:receiving one or more signals based on the trigger, andtemperature-calibrating the XO in a background mode based on thereceived signals.

Another exemplary embodiment is directed to a mobile device comprising:a crystal oscillator (XO), a receiver, and a processor. The processor isconfigured to: determine a temperature-calibration status of the XO,detect a trigger condition related to temperature-calibration of the XO,and if the temperature-calibration status of the XO is not fullytemperature-calibrated, initiate a temperature-calibration session,wherein the temperature-calibration session comprises: enabling thereceiver to receive signals based on the trigger, andtemperature-calibrating the XO in a background mode based on thereceived signals.

Another exemplary embodiment is directed to a wireless communicationsystem comprising: a crystal oscillator (XO), means for receivingsignals, means for determining a temperature-calibration status of theXO, means for detecting a trigger condition related totemperature-calibration of the XO, and means for initiating atemperature-calibration session if the temperature-calibration status ofthe XO is not fully temperature-calibrated, wherein thetemperature-calibration session comprises: receiving one or more signalsbased on the trigger, and temperature-calibrating the XO in a backgroundmode based on the received signals.

Yet another exemplary embodiment is directed to a non-transitorycomputer-readable storage medium comprising code, which, when executedby a processor, causes the processor to perform operations fortemperature-calibrating of a crystal oscillator (XO) in a mobile device,the non-transitory computer-readable storage medium comprising: code fordetermining a temperature-calibration status of the XO, code fordetecting a trigger condition related to temperature-calibration of theXO, and code for initiating a temperature-calibration session if thetemperature-calibration status of the XO is not fullytemperature-calibrated, wherein the temperature-calibration sessioncomprises: receiving one or more signals based on the trigger, andtemperature-calibrating the XO in a background mode based on thereceived signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are presented to aid in the description ofembodiments of the invention and are provided solely for illustration ofthe embodiments and not limitation thereof.

FIG. 1 illustrates a simplified schematic diagram of a device comprisinga XO for field calibration using exemplary embodiments.

FIG. 2 illustrates a flowchart corresponding to a method of XO fieldcalibration using exemplary embodiments.

FIG. 3 illustrates an exemplary implementation of a wirelesscommunication device configured for XO field calibration using exemplaryembodiments.

DETAILED DESCRIPTION

Aspects of the invention are disclosed in the following description andrelated drawings directed to specific embodiments of the invention.Alternate embodiments may be devised without departing from the scope ofthe invention. Additionally, well-known elements of the invention willnot be described in detail or will be omitted so as not to obscure therelevant details of the invention.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. Likewise, the term “embodiments ofthe invention” does not require that all embodiments of the inventioninclude the discussed feature, advantage or mode of operation.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of embodiments ofthe invention. As used herein, the singular forms “a”, “an”, and “the”,are intended to include the plural forms as well, unless the contextclearly indicates otherwise. It will be further understood that theterms “comprises”, “comprising”, “includes”, and/or “including”, whenused herein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Further, many embodiments are described in terms of sequences of actionsto be performed by, for example, elements of a computing device. It willbe recognized that various actions described herein can be performed byspecific circuits (e.g., application specific integrated circuits(ASICs)), by program instructions being executed by one or moreprocessors, or by a combination of both. Additionally, these sequence ofactions described herein can be considered to be embodied entirelywithin any form of computer readable storage medium having storedtherein a corresponding set of computer instructions that upon executionwould cause an associated processor to perform the functionalitydescribed herein. Thus, the various aspects of the invention may beembodied in a number of different forms, all of which have beencontemplated to be within the scope of the claimed subject matter. Inaddition, for each of the embodiments described herein, thecorresponding form of any such embodiments may be described herein as,for example, “logic configured to” perform the described action.

While the uncompensated XO suffers from drawbacks that were previouslyexplained, it is seen in exemplary embodiments that due to severaladvantageous aspects, such as low cost and small size, an uncompensatedXO is a desirable candidate in modern mobile device applications. Inorder to overcome the problems with large frequency variation of theuncompensated XO, the XO can be calibrated, wherein calibration (andmore particularly, “temperature-calibration”) comprises determining ahighly accurate relationship between frequency and temperature for theXO by using assistance from wireless signals of known frequency. Bytemperature-calibrating the XO and establishing a frequency-temperaturerelationship for the XO in this manner, a highly accurate frequencyestimate of the XO can be obtained at any given temperature ofoperation, and thus, the problem of large frequency variations withtemperature can be overcome or compensated for.

With temperature-calibration of the XO, it may be additionallydesirable, in exemplary embodiments, to have the XOtemperature-calibrated to a high degree of accuracy before applicationswhich rely on the accuracy of the XO are launched on the devicecomprising the XO. In some cases, this means that it is desirable totemperature-calibrate the XO prior to launch of position basedapplications using assistance of wireless signals, or in some specificcases, prior to or corresponding to an imminent launch of GNSS sessionsor GNSS applications. One or more exemplary embodiments are accordinglydirected to temperature-calibration of the XO prior to, or based upon animminent, launch of GNSS sessions.

Embodiments described herein may generally pertain to a crystaloscillator (XO) in a device configured for GNSS or GPS applications.More particularly, an exemplary XO is “uncompensated,” which refersherein to an XO which lacks built-in temperature or voltage compensation(or in other words, an XO which comprises a lack of built-incompensation) to account for frequency variation, in contrast to theaforementioned TCXO and VCTCXO, which have temperature and/or voltagecompensation on the TCXO and/or VCTCXO device. The description ofembodiments may simply make reference to an XO, and it will beunderstood hereinafter that such a reference will pertain to anuncompensated XO, unless otherwise specified. Therefore, exemplaryembodiments may be configured to overcome the problem associated withlarge frequency variation in the XO by temperature-calibrating the XOprior to launch of GNSS applications, or in other words, without waitingfor explicit initiation field calibration following the launch of thefirst GNSS session. As used herein, GNSS sessions can includeapplications such as positioning, tracking, mapping, or otherlocation/position based applications using wireless signals receivedfrom satellite sources or sometimes, calibrated terrestrial sources suchas wireless wide area networks (WWAN), code division multiple access(CDMA), long term evolution (LTE) networks. In some embodiments,temperature-calibration of the XO prior to launch of GNSS sessions mayalso mean temperature-calibration of an exemplary XO as early aspossible after the device comprising the XO is taken out of the box andmade ready for use (e.g., by powering on the device for the first time).As will be explained below, some embodiments are also configured toperform this temperature-calibration based on exemplary triggeringconditions, mechanisms, or events and in a background mode.

Before a further detailed explanation of the embodiments is undertaken,additional definitions of terms used in this disclosure will beprovided. As used herein, the term “calibration,” or more specifically,“temperature-calibration,” pertains to a relationship between frequencyand temperature (also known as a “frequency-temperature relationship” or“FT relationship” or “FT model” or “FT curve”) of the XO, formulated toa high degree of accuracy, whereby the frequency of the XO can bedetermined from the formulated relationship at any given temperature.While in some cases, the more general term, “calibration,” may be used,it will be understood that “calibration” refers to“temperature-calibration” as it pertains to the exemplary embodiments,wherein temperature-calibration generally means determination of an FTrelationship or FT model for the XO. Moreover, temperature-calibrationof the XO in exemplary embodiments may also be distinguished fromprecalibration of the XO during manufacture or in factory settings.Precalibration, factory-based calibration, or hereinafter,“factory-calibration,” as used herein, pertains to calibration of the XOin factory settings before it is placed in the field or underoperational conditions. Factory-calibration is limited to the frequencyoffset at nominal temperature. Calibrating each XO across a broad rangeof temperatures in the factory is time and cost prohibitive. Therefore,factory-calibration is generally insufficient for reliable operation ofthe device during operation or in field conditions. Therefore,embodiments are directed to field-calibration, or more specifically,temperature-calibration in the field, of the XO, which pertains totemperature-calibrating the XO during operation of the device comprisingthe XO, after the device has left the factory, is integrated into amobile device, and is put in use, for example, by the end user of themobile device. Accordingly, it will be understood that the term“calibration” as used herein, refers to field-calibration, and morespecifically, temperature-calibration in the field, during operation ofthe device, and excludes any precalibration that may exist in the XO.

In general, an exemplary XO can be temperature-calibrated using one ormore wireless signals of known frequency, wherein the wireless signalsmay be satellite signals (e.g., GNSS signals), or signals from acalibrated terrestrial source such as, WWAN, CDMA, etc. Frequencyassistance can be derived from these wireless signals to estimate afrequency of the XO at a given temperature, and thereby the XO frequencyand temperature can be correlated to form frequency-temperature samples.Using one or more such samples, it is possible to formulate amathematical fit or relationship such as a polynomial equation which canprovide with high accuracy, the frequency of the XO at any giventemperature. This process of formulating the polynomial equation, forexample, comprises temperature-calibration of the XO.

In this disclosure, one or more exemplary embodiments are described,which relate to temperature-calibration of an XO in a background modeand as early as possible out of the box, wherein thetemperature-calibration may be performed using assistance from one ormore wireless signals. Accordingly in some embodiments, one or moretrigger conditions may cause the initiation of temperature-calibrationof the XO in the field, The one or more conditions may relate todetermining whether XO calibration, or more specifically, XO fieldcalibration, has been previously performed and/or if the XO has beenfully calibrated (e.g. precalibrated in the factory) ortemperature-calibrated to desired accuracy. As used herein, the term“not fully temperature-calibrated” refers to a temperature-calibrationstatus of an XO which has not been previously temperature-calibratedand/or not fully temperature-calibrated (in some cases, specificallywith regard to temperature-calibration for position bases application).If it is determined that the XO is not fully temperature-calibrated,exemplary trigger conditions may be generated to initiate atemperature-calibration session of the XO in the field or during deviceoperation. In some embodiments, exemplary temperature-calibration can beperformed in a background mode, i.e. operations pertaining to thetemperature-calibration can be initiated and carried out independentlyfrom any other application or process that may be active in the devicewhich comprises the XO. However, as discussed herein, a background modeneed not be limited to a dedicated temperature-calibration operation,but can include any mode of operation which does not specificallyrequire an active GNSS session or GNSS based application which wouldpossibly or potentially initiate XO temperature-calibration as a matterof course in conventional GNSS based systems. Various exemplary triggersor trigger conditions which can be generated to launchtemperature-calibration to improve user experience, efficiency, andprecision of GNSS sessions, will be described with regard to one or moreconditions for generating the triggers, with reference to exemplaryembodiments below.

As previously explained, temperature-calibration of the XO can involvethe formulation of a frequency-temperature (FT) model or FT curve. TheFT model can be expressed as a polynomial equation or function, whereinfrequency is expressed as an n^(th) degree polynomial function oftemperature. At least some of the parameters or coefficients of thispolynomial equation are unknown quantities for an XO and accordingly, anobjective of the XO temperature-calibration can comprise determining orrefining the coefficients of the FT model for the XO. Using the receivedwireless signals of known frequency and an associated temperaturesensor, processors on the device can be configured to obtain frequencyestimates for the XO from the received wireless signals and associatethem with temperature to form sample points comprising frequency andtemperature for the XO. With sufficient sample points, the polynomialequation (or any other pre-specified mathematical fit of the frequencyand temperature for the XO) can be solved, or in other words, theunknown coefficients can be determined. In general, the number ofcoefficients will vary proportionally with the value of “n” or thedegree of the polynomial. However, in exemplary embodiments, certainconstraints can be imposed to make reasonable assumptions regarding thevalue of one or more coefficients, such that the number of coefficientsthat are unknown, and need to be determined, may be reduced. In anotherexample, a subset of all the parameters of the polynomial equation maybe known in advance, based for example on an XO data sheet and/or an XOcharacteristics specification from XO vendors, thereby also reducing thenumber of unknown coefficients to be determined. The number of samplepoints required for the temperature-calibration may be reduced byreducing the number of unknown coefficients, and accordingly, theprocess of temperature-calibration can be speeded up. Once all theunknown coefficients are determined, the temperature-calibration can besaid to be completed, or the XO can be referred to as atemperature-calibrated XO. Therefore, an XO which is not fullytemperature-calibrated may be an XO for which one or more coefficientsare unknown, insufficiently determined or otherwise need to bedetermined.

Exemplary embodiments can relate to detecting trigger conditions forinitiating temperature-calibration using received wireless signals, in abackground mode. The following description of exemplary embodiments willgenerally include a description of the various triggers for initiatingtemperature-calibration. One or more of these triggers or triggerconditions can be detected in combination in any particular embodiment,and embodiments are not restricted detection of any single triggercondition. Moreover, the embodiments are not restricted to any singletriggering condition for or particular manners of detecting or using thetriggers and skilled persons may choose any manner, or combinationthereof, for implementing the exemplary triggers, without departing fromthe scope of the disclosed embodiments. It will also be understood thatwhile the terms “trigger” or “trigger condition” (which may be usedinterchangeably herein) may in some cases refer to a logical signalwhich may be transmitted or transferred from one logical block toanother in order to initiate a temperature-calibration session, the termmay also refer to a condition code or a logical state where a relatedcondition has been satisfied. The particular meaning of the term willbecome apparent based on the context in which the particular embodimentsare described.

With reference to FIG. 1, a simplified schematic of an exemplary device100 configured for XO field calibration according to exemplaryembodiments is illustrated. It will be noted that device 100 may pertainto a mobile device or handheld device and may further comprise one ormore components as known to one skilled in the art, but which are notillustrated in FIG. 1, for the sake of clarity (although FIG. 3 providesother exemplary embodiments directed to devices similar to device 100,which illustrate certain other components which may be included in theexemplary devices). Device 100 may comprise receiver 102, which may beconfigured to receive wireless signals from various sources such as, oneor more signal sources 110 a-n. In one non-limiting example, one or moreof signal sources 110 a-n may be satellite or GNSS sources capable ofproviding GNSS fixes, including geo-stationary sources such as asatellite based augmentation system (SBAS). Additionally and optionally,one or more signal sources 110 a-n may also be calibrated terrestrialsources, such as WWAN or CDMA. Receiver 102 may be driven by clock 104which can be sourced from XO 106. Temperature sensor 114 may be includedin device 100 to sense temperature of XO 106 and provide XO manager 108with operating temperature associated with XO 106. XO manager 108 may beconfigured to obtain frequency estimates for XO 106 based on signalsreceived by receiver 102. XO manager 108 may be further configured toassociate operating temperatures provided by temperature sensor 114, andperform operations related to temperature-calibration of XO 106according to the above-described techniques. While XO manager 108 isdesignated as a separate block in this illustration, the functionalityand logic associated with XO manager 108 may be integrated in anyprocessor, such as a digital signal processor or a general purposeprocessor (not explicitly shown in FIG. 1), in device 100.

In FIG. 1, one local oscillator, local oscillator 112, is illustrated asincluded in receiver 102. Local oscillator 112 may be sourced from XO106, such that a frequency variation in local oscillator 112 may beproportional to frequency variation of XO 106 with temperature. In thevarious embodiments described herein, one or more other localoscillators may also be present in one or more other blocks. For example(as will be further described with reference to FIG. 3), an exemplarymobile device may comprise one or more receivers or transceiversconfigured for reception of satellite signals and one or more receiversor transceivers configured for other wireless signals such as WWANsignals. Accordingly, in some embodiments, each of those receiversand/or transceivers may have one or more local oscillators. At a giventemperature, frequency of the one or more local oscillators, such as,local oscillator 112, can be compared with the frequency of receivedwireless signals to arrive at an estimate of frequency of XO 106, inorder to generate the frequency-temperature samples required fortemperature-calibration of XO 106.

In one exemplary configuration, XO manager 108 may initiate operationsrelated to temperature-calibration or a temperature-calibration sessionof XO 106 based on exemplary triggers or triggering conditions. In oneexample, initiation of temperature-calibration of XO 106 may betriggered using one or more mechanisms or conditions which will bedescribed in detail in the following sections. In some embodiments,logic for detecting and responding to the trigger conditions accordingto various triggering mechanisms, for example, based on temperaturesensor 114, may be located anywhere on device 100, including within XOmanager 108, although such logic is not explicitly illustrated. Skilledpersons will understand various techniques for implementing andgenerating exemplary triggers based on the disclosure herein. Based on areceived triggering condition, in one embodiment, XO manager 108 maysend a command or logical signal to receiver 102 in order to informreceiver 102 to start searching for and/or receiving wireless signals,such as GNSS signals. In another embodiment, the trigger condition maybe used to enable receiver 102 to commence searching/receivingfunctions.

The trigger conditions may be based on a condition which relates totemperature-calibration of XO 106, wherein the condition ensures thattemperature-calibration of XO 106 is performed at first use of device100, or as early as possible after device 100 is first turned on ortaken out of the box, and in some cases, prior to launch of a positionbased or GNSS based application (i.e. an application other than theabove-described process of XO calibration using GNSS signals). In somecases, the trigger condition can accordingly relate to an imminentlaunch of a position based application or a GNSS based application. Forexample, the trigger condition comprising the first use of device 100may be detected based on an indication associated with powering ondevice 100. As seen in further embodiments, once XO 106 is fully orcompletely temperature-calibrated, the temperature-calibration status ofXO 106 will be updated to reflect that XO 106 is temperature-calibrated.Thus, the status of temperature-calibration can be combined with anindication of powering on device 100 as a trigger condition related tofirst use for initiating temperature-calibration of XO 106, in order toensure that subsequent power-on operations will not keep repeatedlytriggering temperature-calibration if the XO is fullytemperature-calibrated, by updating the status of the XO to reflect thatit is completely temperature-calibrated after temperature-calibration iscomplete. In some embodiments which will be further described in thefollowing sections, subsequent power-on operations can contribute toconditions related to triggering temperature-calibration, if some othercriteria are met, for example, if a pre-specified time has elapsed sinceprevious temperature-calibration of the XO or if a pre-specifiedfrequency error in the local oscillator or XO frequency is exceeded. Inone embodiment, XO manager 108 may enable temperature-calibration of XO106 in a background mode based on a detection of the condition thatdevice 100 is first powered on out of the box. As previously discussed,temperature-calibration of XO 106 in the background mode relates toperforming operations pertaining to temperature-calibration in parallelwith one or more other/unrelated processes or functions that can beperformed in device 100 (for example using processing components ofdevice 100 which are not illustrated in FIG. 1 without interfering withor depending on the operations pertaining to temperature-calibration).

In one embodiment, the condition for generating a trigger may pertain tocharging of device 100. For example, a condition or state of device 100can be detected to indicate that device 100 is turned on and ischarging. In exemplary embodiments, such a state can be detected byusing hardware, software, or firmware to determine that device 100 isconnected to a power outlet, and this state may be utilized to triggertemperature-calibration of XO 106. In one implementation, XO manager maymake the determination using input related to detection of device 100being in a charging state and may internally generate a trigger signal.It will be recognized that this embodiment can have several beneficialaspects. For example, it will be recognized that many handheld devicesare packaged and delivered to end users in an uncharged or minimallycharged state. Accordingly, the users may need to first plug in orcharge the device before first use as a matter of course. Triggeringtemperature-calibration by detecting the trigger condition that device100 is being charged, can accordingly satisfy the condition thattemperature-calibration is performed when device 100 is fresh out of thebox, prior to launching, or based upon an imminent launch of a positionbased or GNSS based application on device 100. Additionally oralternatively, the triggering condition may satisfy the condition thatthe calibration status of XO 106 is not-fully temperature-calibrated (ortemperature-calibration has not been previously performed for XO 106).In another advantageous aspect of this embodiment, charging device 100can cause thermal variations or heating in device 100, which can provideseveral different operating temperature samples as are needed forformulation of the FT curve or calibration of XO 106. Yet anotheradvantageous aspect of this embodiment can relate to power savings, inthat, the temperature-calibration process is performed while device 100is still plugged in, and therefore does not lead to a drain on batteryresources. The related benefits may be significant because the processof temperature-calibration may require long periods of searching for andacquiring signals of sufficient strength and quality (e.g. as may bedetermined using threshold signal to noise (SNR) ratio criteria anderror/parity checks respectively in some embodiments), which will berecognized by the skilled person as a power hungry process. Accordingly,performing such a power hungry process while device 100 is plugged in,rather than when it is being used on battery power may save on batterylife.

In a related embodiment, temperature-calibration may be triggered basedon conditions, or indications related to temperature or variation intemperature, while not necessarily requiring the condition that device100 is plugged in or is in a charging state. In this embodiment,temperature of device 100, may be tracked, for example, usingtemperature sensor 114. When variation in temperature is detected acrossa period of time, a related trigger condition may be detected, forexample by XO manager 108 based on inputs from temperature sensor 114.In one implementation, operating temperature may be recorded at initialconditions or at a first point in time. At a second point in time, if acomparison of the temperature provided by temperature sensor 114 withthe recorded temperature reveals that the temperature has changed fromthe first point in time, the trigger condition may be detected onceagain. In addition, the triggering condition(s) may be based uponreaching or exceeding particular temperatures of XO 106. Thesetemperatures, also known herein as “triggering temperatures” can bepre-specified, for example, to provide an optimal spread of samplepoints. The triggering temperatures can also be determined randomly oractively to obtain sample points at temperatures that are different fromthose already sampled or used in sample points. In one example, when thetriggering temperature is reached, and if XO 106 is not fullytemperature-calibrated, an XO temperature-calibration session may beinitiated. In this manner, wireless signals may be received by receiver102 at different sample operating temperatures and frequency estimatesmay be derived to form frequency-temperature samples at differentoperating temperatures for the process of temperature-calibration.

In another embodiment, the temperature-calibration may be triggeredbased on a trigger condition comprising the presence of device 100 in anoutdoor location or outdoor environment or with a clear view to the sky.This embodiment relates to the availability of at least one strongreceived signal, such as a strong GNSS signal, from signal sources 110a-n when device 100 is outdoors or with a clear or unobstructed view tothe sky. Several mechanisms related to the trigger conditions may beused in this embodiment. In a first example, the trigger condition canbe based on strength of the GNSS signals received at receiver 102, forexample, because strong signal strength can indicate that device 100 ispresent in an outdoor location, and thus can be used initiatetemperature-calibration of XO 106. In a second example, the triggercondition can comprise detecting a pre-designated velocity of device100. A speed sensor, speedometer, or accelerometer (not shown)associated with device 100 can detect whether device 100 is in motion,and moreover, an indication of high speed/velocity or whether the speedof motion is high enough to relate to those of automobiles on highways.If device 100 is detected to be in motion, based, for example, ondetecting a pre-designated velocity of device 100, it may be estimatedby XO manager 108 that there is a high likelihood of device 100 beinglocated in an automobile travelling on a road or highway, and thereforebeing present in an outdoor location or environment with strong GNSSsignals. Detecting the pre-designated velocity may also be based onDoppler measurements of the GNSS signals, because in some instances,rapidly varying Doppler values can be a characteristic of device 100being in motion at a high velocity. In a third example, the triggercondition comprises detecting sunlight or strong sun rays incident ondevice 100. A light sensor (not shown) associated with device 100 maydetect sunlight or strong rays incident on device 100 to estimate thatdevice 100 is in an outdoor environment, and send a related notificationto XO manager 108, which may thereby detect the trigger condition basedon the notification. In a fourth example, the trigger condition cancomprise pre-specified times or periodic alerts based on a local clock,such as clock 104 or any other clock associated with device 100. In thisfourth example, a pre-specified time of day or night, such as 8ΔM, noon,6 PM, etc. may be used as guidelines to guess that the user of device100 may be outdoors, for example, travelling between home and work.Alternately, a time, for example, midnight, can be used as a triggercondition to initiate a temperature-calibration session when device 100is not in use and likely to be on a charger. Further customization maybe based on a specific user's needs or personal information. In a fifthexample, the trigger condition can comprise user input. The user ofdevice 100 can input an indication, for example, through designatedinterfaces, ports, or other input mechanisms. The input mechanisms caninclude a response to a prompt or a program or application, to receive auser input which can indicate that device 100 is located outdoors orwith a clear view to the sky. Regardless of the exemplary triggerconditions used for triggering calibration of XO 106, based on a highlikelihood of device 100 being present in an outdoor environment or witha clear/unobstructed view of the sky, the related embodiments maybeneficially contribute to efficient and fast XO calibration because ifstrong GNSS signals are available then the temperature-calibrationprocess using received GNSS signals may be fast and accurate.

One or more of the above described embodiments can involvetemperature-calibration in a background mode. As previously noted,temperature-calibration in a background mode can relate totemperature-calibration performed independently of position based orGNSS based applications. In some cases, device 100 can be configured tosupport parallel processes, wherein temperature-calibration can becarried out in a process without interfering with or depending on anyother process or application being executed by device 100. In someexamples, temperature-calibration can be performed based on wirelesssignals received from geo-stationary sources such as a single SBASvehicle, as the SBAS signals have advantageous characteristics, such aszero Doppler, which can expedite or improve the temperature-calibrationin some cases. Therefore, an exemplary trigger condition for initiatingtemperature-calibration of XO 106 can comprise detecting that a SBASvehicle is within the view of or with a clear path to device 100. XOmanager 108 can be alerted to initiate temperature-calibration of XO 106based on a high confidence acquisition of the SBAS signal. Detectingthat a SBAS vehicle is within clear view of device 100 can be achievedby detecting SBAS signals received, for example, at receiver 102, andmeasuring the strength of the received SBAS signals. Similar advantagesmay be obtained by a stationary device using terrestrial signals ofknown frequency for temperature-calibration of XO 106, such thatdetecting that the device is stationary, as well as, detecting strongterrestrial signals of known frequency, can be used to triggertemperature-calibration of XO 106.

In some embodiments, prior to initiating a temperature-calibrationsession based on one or more above-described trigger conditions, a checkmay be performed on the temperature-calibration status of XO 106 toensure that XO 106 is not fully/completely temperature-calibrated orthat a pre-specified time has elapsed since XO 106 was lasttemperature-calibrated. Thus, needless, redundant, or in some cases,conflicting operations can be avoided. Accordingly, in oneimplementation, a status indication or flag may be provided in XOmanager 108 related to temperature-calibration status of XO 106. Thestatus indication may be stored, for example, in a storage means such asa register (not explicitly shown), which may be situated within XOmanager 108 or any other suitable storage medium. If XO 106 had beentemperature-calibrated, for example, based on one or more triggerconditions, then the temperature-calibration status ortemperature-calibration flag would have been updated to indicate thestatus as “temperature-calibrated.” A subsequent or second trigger,based for example, on a subsequent or second condition related totemperature-calibration of XO 106 will be suppressed or prevented frominitiating a temperature-calibration session for XO 106. On the otherhand, if the temperature-calibration flag indicates that thetemperature-calibration status of XO 106 is “not fullytemperature-calibrated,” then a second trigger condition may bedetected, and a second temperature-calibration session may be initiated.In another example, the temperature-calibration flag may be accompaniedby or replaced with a recorded time of previous temperature-calibration.An aspect of the recorded time of previous temperature-calibrationcomprises designating a pre-specified time associated with quality oftemperature-calibration, such that, if the pre-specified time haselapsed since the recorded time of previous temperature-calibration, XO106 may be treated as not fully temperature-calibrated. This aspect isbased on the characteristic of mechanical structures like XO 106 todegrade in quality over time, and more specifically a characteristic ofXO 106 to lose precision of temperature-calibration. Accordingly, uponeach successful/complete temperature-calibration of XO 106, the time(e.g. based on any clock, such as clock 104, on device 100) at whichtemperature-calibration was completed may be recorded or stored in astorage means such as a register or memory. Upon detection of a triggercondition, the recorded time may be consulted, and if the pre-specifiedtime has elapsed, the temperature-calibration status of XO 106 may bedesignated as not fully temperature-calibrated. The pre-specified timemay be based on individual specifications of XO crystals, and may bebased on information provided by the manufacturer.

In another embodiment, the temperature(s) at whichtemperature-calibration was performed can be recorded andtemperature-calibration may be triggered only if a trigger condition isdetected at a temperature different from the recorded temperature(s) orif, as noted above, a pre-specified time has elapsed sincetemperature-calibration may have been previously performed at thecurrent temperature. This latter embodiment may prevent alwaysinitiating temperature-calibration at start up or power up of device100, even when XO 106 is not fully temperature-calibrated, if thetemperature at the start up is the same as the current temperature andtemperature-calibration would result in needlessly duplicating existingsamples.

In one example pertaining to trigger conditions based ontemperature-calibration status, XO manager 108 may first clear thetemperature-calibration status registers or temperature-calibrationflags at an initial point in time. If a first trigger condition isdetected based on device 100 being in a charging state,temperature-calibration of XO 106 is performed pursuant to this firsttrigger condition. Upon completion of the temperature-calibration, thestored temperature-calibration status in the temperature-calibrationstatus registers may be updated or recorded as full/complete or“temperature-calibrated”. In some embodiments, the time at whichcalibration was completed, may be recorded as the firsttemperature-calibration time, in addition to and along with, or insteadof, the temperature-calibration status in the temperature-calibrationstatus registers. If a subsequent condition is detected, for example,based on light sensors indicating that device 100 is in an outdoorenvironment, then XO manager 108 may consult the temperature-calibrationstatus registers and/or the recorded time. In the case when recordedtime of previous temperature-calibration is not available, thetemperature-calibration status registers may indicate that XO 106 hasalready been temperature-calibrated, and generation of another triggermay be suppressed. In embodiments which utilize the aspect of therecorded time of previous temperature-calibration, XO manager 108 mayadditionally or alternatively consult the recorded time, and compare theinstant time at which the condition related to device 100 being in anoutdoor environment is detected, to the first temperature-calibrationtime. If a pre-specified time has elapsed, XO 106 may be treated as notfully temperature-calibrated, and the related trigger condition may bedetected. If the pre-specified time has not elapsed, then XO 106 may betreated as temperature-calibrated, and the trigger condition may benegated or suppressed in order to avoid unnecessary and redundantre-calibration of XO 106. In some cases, XO manager 108 may beconfigured to proactively perform status checks, wherein if XO 106 hasnot been temperature-calibrated for at least the pre-specified time, orin other words, the pre-specified time has elapsed since the recordedtime of previous calibration, then XO manager 108 may demote thetemperature-calibration status of XO 106 to not fullytemperature-calibrated. Accordingly, the temperature-calibration statusof XO 106 may be based on keeping track of time elapsed from recordedtime of previous temperature-calibration, and updating thetemperature-calibration status to not fully temperature-calibrated, evenwhen an intervening condition related to temperature-calibration, whichwould generate a trigger, has not been detected. As will be recalledfrom the embodiment wherein the trigger condition for initiatingtemperature-calibration of XO 106 is based on powering on device 100 forthe first use following the first time device 100 is powered on out ofthe box, the temperature-calibration status registers may be cleared atthose initial conditions, such that a trigger condition may be detectedand temperature-calibration of XO 106 may be initiated as soon aspossible after device 100 is first powered on. Oncetemperature-calibration is completed following the first time device 100is powered, on, the time at which this temperature-calibration wasperformed can be recorded. For subsequent times that device 100 ispowered on, unless the pre-specified time has elapsed, XO manager may beconfigured such that trigger conditions relating to powering on device100, may themselves not be sufficient to initiatetemperature-calibration or repeated temperature-calibration of XO 106.Thus, needless temperature-calibration can be avoided every time device100 is powered on, unless the pre-specified time, indicating forexample, degradation in quality of temperature-calibration of XO 106,has elapsed.

It will be appreciated that embodiments include various methods forperforming the processes, functions and/or algorithms disclosed herein.For example, as illustrated in FIG. 2, an embodiment can include amethod of temperature-calibration in a mobile device, the methodcomprising: determining a temperature-calibration status of the XO (e.g.by reading the aforementioned temperature-calibration status registersand/or recorded time of previous temperature-calibration)—Block 202;detecting a trigger condition related to temperature-calibration of theXO (e.g. conditions comprising launching a position based application ortemperature-calibrating XO 106 prior to launching or based on animminent launch of a position based application on device 100; chargingdevice 100; varying operating temperature associated with device 100;device 100 being present in an outdoor location, based for example ondetection of at least one strong GNSS signal or strong sun rays,detecting a pre-designated velocity of device 100, based for example, onDoppler measurements of GNSS signals or output from a speedometerassociated with device 100, a pre-specified time associated with device100; a user input, etc.)—Block 204; if the temperature-calibrationstatus of the XO is not fully temperature-calibrated (e.g. based ontemperature-calibration status provided in the temperature-calibrationstatus registers and/or whether a pre-specified time has elapsed sincethe recorded time of previous temperature-calibration), initiating atemperature-calibration session, (e.g. using a logical signal or commandfrom XO manager 108 to receiver 102 or condition code to enable receiver102 or initiate reception of signals at receiver 102) wherein thetemperature-calibration session comprises: receiving one or more signalsbased on the trigger (e.g. at receiver 102 from signal sources 110 a-n,which may be GNSS sources, calibrated terrestrial sources such as WWAN,and/or geo-stationary sources such as SBAS sources, wherein any one ormore of the signal sources may be used to generate a GNSS fix or provideGNSS time for purposes of temperature-calibrating XO 106)—Block 208; andtemperature-calibrating the XO in a background mode based on the one ormore received signals (e.g. performing operations related to formulatingof the FT model and associated parameters related to XO 106 in abackground mode of operation which does not specifically require anactive GNSS session or GNSS based application which would possiblyinitiate temperature-calibration as a matter of course in conventionalGNSS based systems)—Block 210.

With reference now to FIG. 3, another exemplary device 300 implementedas a wireless communication system is illustrated. Device 300 is similarto device 100 in many exemplary aspects, and the depiction anddescription of device 300 includes various additional exemplarycomponents not shown with relation to device 100 in FIG. 1. As shown inFIG. 3, device 300 includes digital signal processor (DSP) 364 and ageneral purpose processor, depicted as processor 365. Theabove-described functions and methods related to temperature-calibrationcan be performed in DSP 364 or processor 365 or any combination of theprocessing elements thereof. Accordingly, in some embodiments, processor365 may be configured to perform operations described with regard to XOmanager 108, but it will be understood that some of the operationsrelated to temperature-calibration can be performed in DSP 364, andmoreover, these operations can be implemented in any suitablecombination of hardware and software. Both DSP 364 and processor 365 maybe coupled to clock 104 driven by XO 106 as previously described and tomemory 332. Instructions related to related to a coder/decoder (CODEC)334 (e.g., an audio and/or voice CODEC) can be stored in memory 332.Speaker 336 and microphone 338 can be coupled to audio controller 334,which can be coupled to processor 365 and/or to DSP 364. Displaycontroller 326 can be coupled to DSP 364, processor 365, and to display328. Other components, such as transceiver 340 (which may be part of amodem) and receiver 341 are also illustrated. Transceiver 340 can becoupled to wireless antenna 342, which may be configured to receivewireless signals from a calibrated terrestrial source such as WWAN,CDMA, etc. Receiver 341 can be coupled to a satellite or GNSS antenna343, which may be configured to receive wireless signals from satellitesor GNSS signals. In some embodiments, both receiver 341 and transceiver340 may include respective local oscillators 112 and 113, which may besourced from XO 106. Temperature sensor 114 is also illustrated, and maybe coupled to clock 104 and processor 365. In a particular embodiment,DSP 364, processor 365, display controller 326, memory 332, audiocontroller 334, transceiver 340, receiver 341, clock 104, andtemperature sensor 114 are included in a system-in-package orsystem-on-chip device 322.

In a particular embodiment, input device 330 and power supply 344 arecoupled to the system-on-chip device 322. Moreover, in a particularembodiment, as illustrated in FIG. 3, display 328, input device 330,speaker 336, microphone 338, wireless antenna 342, GNSS antenna 343, andpower supply 344 are external to the system-on-chip device 322. However,each of display 328, input device 330, speaker 336, microphone 338,wireless antenna 342, GNSS antenna 343, and power supply 344 can becoupled to a component of the system-on-chip device 322, such as aninterface or a controller.

In one embodiment, one or both of DSP 364 and processor 365, inconjunction with one or more remaining components illustrated in FIG. 3,can include logic/means to perform temperature-calibration as discussed,for example, in Blocks 202-208 of FIG. 2. For example, DSP 364 and/orprocessor 365 (illustrated as comprising XO manager 108), can includelogic/means to implement functions related to determining atemperature-calibration status of XO 106, for example, by reading theaforementioned temperature-calibration status registers and/or recordedtime of previous temperature-calibration, which may be stored in memory332 or internally within processor 365. Further, DSP 364 and/orprocessor 365 in conjunction with various other components can includelogic/means for detecting a trigger condition related totemperature-calibration of the XO. For example, conditions comprisinglaunching a position based application or temperature-calibrating XO 106when device 300 is fresh out of the box or prior to launching, or basedupon an imminent launch, of a position based application on device 300can be detected by logic/means associated with power supply 344 toindicate that XO 106 is powered on (as previously noted, this conditioncan be limited in some cases to the first powering on of device 300 outof the box, while subsequent powering on operations will not give riseto this condition); conditions related to charging device 300 can bedetected by logic/means associated with power supply 344; conditions fordetecting varying operating temperature associated with device 300 canbe detected by logic/means associated with temperature sensor 114;conditions pertaining to device 300 being present in an outdoorlocation, can be detected by logic/means such as GNSS antenna 343 todetect at least one strong GNSS signal, or logic/means, such as aspeedometer (not shown) for detecting a pre-designated velocity ofdevice 300, or logic/means in processor 365 for measuring Doppler ofGNSS signals received via receiver 341, logic/means for detectingconditions related to a pre-specified time associated with device 300,such as based on clock 104; logic/means for detecting conditions relatedto a user input, such as via input device 330, etc.). DSP 364 and/orprocessor 365 can include logic/means for determining if thetemperature-calibration status of that XO 106 is not fullytemperature-calibrated (e.g. based on temperature-calibration statusprovided in the temperature-calibration status registers stored inprocessor 365 or memory 332 and/or whether a pre-specified time haselapsed since the time of previous temperature-calibration recorded in astorage means within processor 365 or in memory 332). Based on thedetermination of the temperature-calibration status, processor 365 cancomprise logic/means for initiating a temperature-calibration session(e.g., using a logical signal or command from processor 365 to receiver341 and GNSS antenna 343 or condition code to enable receiver 341 orinitiate reception of signals at GNSS antenna 343). During thetemperature-calibration session, receiver 341 and/or antenna 343 cancomprise logic/means for receiving one or more signals (e.g. from signalsources 110 a-n, which may be GNSS sources, calibrated terrestrialsources such as WWAN, and/or geo-stationary sources such as SBASsources, wherein any one or more of the signal sources may be used togenerate a GNSS fix or provide GNSS time for purposes oftemperature-calibrating XO 106). DSP 364 and/or processor 365 cancomprise logic/means for temperature-calibrating XO 106 in a backgroundmode based on the one or more received signals (e.g. performingoperations related to formulating of the FT model and associatedparameters related to XO 106 in a background mode of operation whichdoes not specifically require an active GNSS session or GNSS basedapplication which would possibly initiate temperature-calibration as amatter of course).

It should be noted that although FIG. 3 depicts a wirelesscommunications device, DSP 364, processor 365, and memory 332 may alsobe integrated into a device, selected from the group consisting of aset-top box, a music player, a video player, an entertainment unit, anavigation device, a communications device, a personal digital assistant(PDA), a fixed location data unit, or a computer. Moreover, such adevice may also be integrated in a semiconductor die.

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The methods, sequences and/or algorithms described in connection withthe embodiments disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module may reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, hard disk, a removabledisk, a CD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

Accordingly, an embodiment of the invention can include a computerreadable media embodying a method for background temperature-calibrationof a XO. Accordingly, the invention is not limited to illustratedexamples and any means for performing the functionality described hereinare included in embodiments of the invention.

While aspects of the above-described embodiments are generally describedin relation to GNSS-based positioning systems, it will be readilyappreciated how these embodiments could be modified to conform withother types of positioning systems, including but not limited tosatellite positioning systems (SPSs) that do not comprise a GNSS,positioning systems that are based upon pseudolites (orpseudo-satellites, e.g., ground-based transceivers) and so on.Therefore, the embodiments described herein can be readily incorporatedwithin non-GNSS-based systems.

While the foregoing disclosure shows illustrative embodiments of theinvention, it should be noted that various changes and modificationscould be made herein without departing from the scope of the inventionas defined by the appended claims. The functions, steps and/or actionsof the method claims in accordance with the embodiments of the inventiondescribed herein need not be performed in any particular order.Furthermore, although elements of the invention may be described orclaimed in the singular, the plural is contemplated unless limitation tothe singular is explicitly stated.

The foregoing disclosed devices and methods are typically designed andare configured into GDSII and GERBER computer files, stored on acomputer readable media. These files are in turn provided to fabricationhandlers who fabricate devices based on these files. The resultingproducts are semiconductor wafers that are then cut into semiconductordie and packaged into a semiconductor chip. The chips are then employedin devices described above.

1. (canceled)
 2. A method of temperature-calibrating a non-temperaturecompensated crystal oscillator (XO) in a mobile device, the methodcomprising: initiating a temperature-calibration session at a poweringon of the mobile device, wherein the temperature-calibration sessioncomprises: receiving wireless signals of a known frequency; andtemperature-calibrating the XO in a background mode based on thereceived wireless signals, in parallel with performing one or moreprocesses unrelated to temperature-calibrating the XO in the backgroundmode, wherein the background mode comprises a mode of operation thatexecutes independently of position based applications or globalnavigation satellite systems (GNSS) based applications.
 3. The method ofclaim 2, wherein the received wireless signals comprise one or more ofglobal navigation satellite systems (GNSS) signals, signals from acalibrated terrestrial source, or signals from a geo-stationary source.4. The method of claim 2, wherein the powering on of the mobile deviceis a first use of the mobile device.
 5. The method of claim 2, furthercomprising updating a temperature-calibration status of the XO ascompleted and suppressing further temperature-calibration based on theupdated temperature-calibration status.
 6. The method of claim 2,further comprising recording a first time associated withtemperature-calibrating the XO and if a pre-specified time has lapsedsince the first time, initiating a second temperature-calibrationsession.
 7. The method of claim 2, wherein temperature-calibrating theXO comprises formulating a frequency-temperature (FT) model based ontemperature-calibrating at a plurality of temperatures.
 8. The method ofclaim 7, wherein the temperature-calibrating further comprisesdetermining coefficients of the FT model for the XO.
 9. The method ofclaim 7, wherein the FT model is expressed as a polynomial function andwherein frequency is expressed as an nth degree polynomial function oftemperature.
 10. The method of claim 2, further comprising: detecting avariation in operating temperature of the mobile device; and initiatinga second temperature-calibration session.
 11. The method of claim 10,wherein the variation in operating temperature is detected over a periodof time.
 12. The method of claim 10, wherein the variation in operatingtemperature is detected based upon reaching or exceeding one or morepredefined temperatures.
 13. The method of claim 10, wherein thevariation in operating temperature is detected based upon randomlyselected temperatures.
 14. The method of claim 2, wherein thetemperature-calibration session is performed prior to the XO being usedfor global navigation satellite systems (GNSS) based applications.
 15. Amobile device comprising: a non-temperature compensated crystaloscillator (XO); a receiver; and a processor configured to initiate atemperature-calibration session at a powering on of the mobile device,wherein the temperature-calibration session is further configured to:receive wireless signals of a known frequency; and temperature-calibratethe XO in a background mode based on the received wireless signals, inparallel with performing one or more processes unrelated totemperature-calibrating the XO in the background mode, wherein thebackground mode comprises a mode of operation that executesindependently of position based applications or global navigationsatellite systems (GNSS) based applications.
 16. The mobile device ofclaim 15, wherein the received wireless signals comprise one or more ofglobal navigation satellite systems (GNSS) signals, signals from acalibrated terrestrial source, or signals from a geo-stationary source.17. The mobile device of claim 15, wherein the powering on of the mobiledevice is a first use of the mobile device.
 18. The mobile device ofclaim 15, further configured to: update a temperature-calibration statusof the XO as completed; and suppress further temperature-calibrationbased on the updated temperature-calibration status.
 19. The mobiledevice of claim 15, further configured to: record a first timeassociated with temperature-calibrating the XO; and if a pre-specifiedtime has lapsed since the first time, initiate a secondtemperature-calibration session.
 20. The mobile device of claim 15,wherein the temperature-calibration session is further configured to:formulate a frequency-temperature (FT) model based ontemperature-calibrating at a plurality of temperatures.
 21. The mobiledevice of claim 20, wherein the temperature-calibration session isfurther configured to determine coefficients of the FT model for the XO.22. The mobile device of claim 20, wherein the FT model is expressed asa polynomial function and wherein frequency is expressed as an nthdegree polynomial function of temperature.
 23. The mobile device ofclaim 15, further configured to: detect a variation in operatingtemperature of the mobile device; and initiate a secondtemperature-calibration session.
 24. The mobile device of claim 23,wherein the variation in operating temperature is detected over a periodof time.
 25. The mobile device of claim 23, wherein the variation inoperating temperature is detected based upon reaching or exceeding oneor more predefined temperatures.
 26. The mobile device of claim 23,wherein the variation in operating temperature is detected based uponrandomly selected temperatures.
 27. The mobile device of claim 15,wherein the temperature-calibration session is performed prior to the XObeing used for global navigation satellite systems (GNSS) basedapplications.
 28. A mobile device comprising: a non-temperaturecompensated crystal oscillator (XO); means for receiving wirelesssignals of a known frequency; and means for initiating atemperature-calibration session at a powering on of the mobile device,wherein the temperature-calibration session comprises: means fortemperature-calibrating the XO in a background mode based on thereceived wireless signals, in parallel with performing one or moreprocesses unrelated to temperature-calibrating the XO in the backgroundmode, wherein the background mode comprises a mode of operation thatexecutes independently of position based applications or globalnavigation satellite systems (GNSS) based applications.
 29. The mobiledevice of claim 28, wherein the received wireless signals comprise oneor more of global navigation satellite systems (GNSS) signals, signalsfrom a calibrated terrestrial source, or signals from a geo-stationarysource.
 30. A non-transitory computer-readable storage medium comprisingcode, which, when executed by a processor, causes the processor toperform operations for temperature-calibrating of a crystal oscillator(XO) in a mobile device, the non-transitory computer-readable storagemedium comprising: code for initiating a temperature-calibration sessionat a powering on of the mobile device, wherein thetemperature-calibration session comprises: code for receiving wirelesssignals of a known frequency; and code for temperature-calibrating theXO in a background mode based on the received wireless signals, inparallel with performing one or more processes unrelated totemperature-calibrating the XO in the background mode, wherein thebackground mode comprises a mode of operation that executesindependently of position based applications or global navigationsatellite systems (GNSS) based applications.
 31. The non-transitorycomputer-readable storage medium of claim 30, wherein the receivedwireless signals comprise one or more of global navigation satellitesystems (GNSS) signals, signals from a calibrated terrestrial source, orsignals from a geo-stationary source.